We used to think the brain was sealed off from the immune system, a fortress behind the blood–brain barrier. That view has collapsed. We now know the brain is in constant dialogue with the body’s defences, and sometimes, the conversation goes badly.
Chronic, low-grade inflammation is emerging as a central player in mental health and brain ageing. Depression, anxiety, even dementia, conditions once explained mainly in psychological or neurological terms, are now being reframed as partly immune disorders.
When the blood–brain barrier weakens under stress or metabolic strain, cytokines leak in. They disrupt dopamine and serotonin, flip microglia from “caretakers” to “arsonists,” and set off vicious cycles of oxidative stress. Meanwhile, the gut also contributes: dysbiosis generates toxins that accelerate systemic inflammation, whereas fibre-rich, Mediterranean-style, whole-food, plant-predominant diets strengthen barriers and dampen the immune load.
Ageing adds another twist. Research in killifish shows ribosomes pausing on certain amino acids, stalling protein production. This “translation failure” slows repair and it triggers inflammatory alarms in the brain itself. In other words, ageing and inflammation are two sides of the same process.
Encouragingly, interventions are multiplying. Exercise and anti-inflammatory diets really do reduce risk, with Mediterranean and whole-food plant based adaptations even shifting Alzheimer’s biomarkers. GLP-1 agonists, better known as diabetes and weight-loss drugs, may work directly in the brain to combat inflammation and cognitive decline. Psychedelics, too, show surprising promise: in stressed mice, psilocybin and MDMA reduced inflammatory cell build-up around the brain and reset fear responses. And on the horizon, ultra-selective vagus nerve stimulators could allow us to modulate the immune system with surgical precision.
The dichotomy between “mental” and “physical” health is now dissolving. The brain is not immune-privileged, it is an immune organ. Depression may be as much about inflammatory tone as about serotonin; dementia as much about immune dysfunction as about plaques.
For patients and clinicians alike, this shifts the framework in which they work. It means that lifestyle choices, movement, food, stress management, carry immune consequences that translate into mood and memory. It means that new therapies may come not from the psychiatrist’s prescription pad alone, but from immunology, neuromodulation, even psychedelic research labs.
What this really offers is a reframing: that protecting the mind is inseparable from calming the body’s chronic inflammatory processes.
Dr Michael Simmons
My Wellness Doctor
My Wellness Doctor 
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